Inflammation is an important defense response occurring in body against pathogens, foreign substances and tissue injury. Inflammation accompanies systemic symptoms such as fever, weakness, loss of appetite and chill, or local symptoms such as redness, swelling, pain and dysfunction. Inflammation is divided into acute inflammation, subacute inflammation and chronic inflammation according to its duration. Acute inflammation reaction occurs in blood vessel and is mostly mediated by neutrophils. Especially, in the case of suppurative inflammation, remarkable increase of neutrophils is observed. Chronic inflammation is continued for several weeks or several months. It is different from acute inflammation in that injury and recovery of tissues occur at the same time (Robbins Pathological Basis of Disease by R. S. Cotran, V Kumar, and S. L. Robbins, W.B. Saunders Co., p. 75, 1989). Although chronic inflammation may be derived directly from acute inflammation, it generally results from continuous infections that cause prolonged hypersensitive reactions (ex., tuberculosis, syphilis, fungal infection), exposure to continuous endotoxin (ex., increased plasma lipids) or exotoxins (ex., silica, asbestos, tar, surgery sutures), or autoimmune response against self-tissues (ex., rheumatic arthritis, systemic lupus erythematosus, multiple sclerosis, psoriasis) and it can thus initiate insidious onset that proceeds as times goes by. Accordingly, chronic inflammation includes numerous medical symptoms such as rheumatic arthritis, restenosis, psoriasis, multicentric sclerosis, surgery synechia, tuberculosis and chronic inflammatory lung diseases (ex., asthma, pneumoconiosis, chronic occlusive lung disease, pulmonary fibrosis). Subacute inflammation refers to an inflammation between acute and chronic inflammations.
As main inflammatory diseases, there are rhinitis and sinusitis such as infectious rhinitis, allergic rhinitis, chronic rhinitis, acute sinusitis and chronic sinusitis; otitis media such as acute purulent otitis media and chronic purulent otitis media; pneumonia such as bacterial pneumonia, bronchopneumonia, lobar pneumonia, Legionella pneumonia and viral pneumonia; acute or chronic gastritis; enteritis such as infectious enterocolitis, Crohn's disease, idiopathic ulcerative colitis and pseudomembranous colitis; and arthritis such as pyogenic arthritis, tuberculous arthritis, degenerative arthritis and rheumatoid arthritis. In addition, there is sepsis that accompanies extreme systemic inflammatory reaction at early stage. This sepsis results from excessive reaction of hosts against endotoxin of gram-negative bacteria, etc. In prior arts, so as to treat sepsis, there have been used antibiotics and steroid preparations, but their effects are weak and thus the death rate of hosts due to septicemia is still high.
Also, excessive inflammation causes permanent injury of surrounding tissues, and acute respiratory distress syndrome (ARDS) is regarded as one of typical inflammatory diseases resulting from tissue injury by excessive inflammation. The ARDS is an acute hypoxemic respiratory failure due to pulmonary edema resulting from the increased permeability of alveolar capillary barrier. It is regarded as the most severe case in acute lung injury (ALI). Clinical symptoms that lead patients to the risk of ARDS are various, for example, trauma, bleedings or septicemia, and ARDS results from excessive systemic inflammation reaction due to these symptoms. Even though there have been conducted treatments such as treatment of hypoxia, endotracheal intubation, mechanical ventilation, etc., the death rate due to ARDS still reaches 50˜70%. Circulating inflammatory cells, especially neutrophils, have been known to have an important role in initiation and development of acute lung injury, e.g., pulmonary edema, inflammation reaction, etc. (Abraham et al., Am. J. Physiol., 279, L1137-L1145, 2000). Several scientists proved that neutrophils are extensively accumulated in lungs of ARDS patients (Weinacker & Vaszar, Annu. Rev Med., 52: 221-37, 2001). These neutrophils, once activated, discharge proteases including matrix metalloproteinases and other mediators causing lung injury. Hence, if neutrophil accumulation in lung is suppressed, ARDS due to acute lung injury may be treated.
Multiple organ dysfunction syndrome (MODS) is a disease resulting from the complication of sepsis, etc. As examples of MODS, there can be included acute hepatic failure, acute renal failure, lung failure, gastrointestinal bleeding, etc. For the treatment of MODS, antibiotics and steroid preparations have been used, however, their effects are weak.
Meanwhile, neutrophils (also called ‘polymorphonuclear leucocytes (PMNs)’) are phagocytic cells that have an important role in host defense mechanism and occupy approximately 60% of leucocytes that are circulating in body. The membrane of neutrophils has receptors for hemopoietic growth factors such as GM-CSF (granulocyte macrophage-colony stimulating factor), G-CSF (granulocyte-colony stimulating factor), etc., G proteins involving in signal transduction associated with receptors for opsonin and chemotactic factors, ion channels associated with the ion exchange of Na+, K+, Ca2+, etc., enzymes and phospholipids. Also, at the surface of neutrophils, there exist Fc receptors against an IgG antibody such as CD16 and CD32 and receptors to C3 complement proteins such as CR1 and CR3. Accordingly, antigens bound thereto can be easily recognized and eliminated. As within the granule of neutrophils, there are defensin associated with disinfection such as peroxidase, lactoferrin, leukocyte adhesion receptor and alkaline phosphatase, and bactericidal/permeability-increasing protein (BPI), which destroy infectious agents or are involved in the proceedings of inflammatory reaction. Besides, the neutrophils express cell adhension proteins such as CD11a/CD18(LFA-1), selectin, etc., which have an important role in the movement of neutrophils in inflammatory reaction.
For a normal adult, neutrophils are produced in an amount of 0.85-1.6×109 cells/kg/day. After being produced and differentiated in bone marrow over approximately 14 days, they enter peripheral bloods and circulate there for about 6 hours. They penetrate then into tissues and die or are lost at mucous membranes after surviving for several days in the tissues. Neutrophils have a short half-life of about 6-10 hours and they are removed in macrophages by apoptosis. The neutrophil apoptosis occurs spontaneously or by the external stimulus. As a typical example of the external stimulus, there can be mentioned a Fas pathway. Fas is a substance similar to TNF receptor that exists at the surface of neutrophils, and it induces apoptosis via an FADD pathway in cells once it is stimulated by a Fas ligand. Caspase has been known to have an important role in such a pathway. Neutrophil apoptosis has been known to be delayed or suppressed by various inflammation mediators. Some reports proposed that the delay (suppression) of neutrophil apoptosis observed in ARDS is due to GM-CSF. However, the intracellular transduction pathway that delays apoptosis of neutrophil had been hardly known. That is, in several inflammatory diseases, various inflammation mediators suppress neutrophil apoptosis that is physiologically and actively occurring, and consequently, continuous inflammatory reaction occurs by excessive neutrophil accumulation resulting in the damage to surrounding tissues. As inflammation mediators, there have been known G-CSF, GM-CSF, IFN-γ, IL-2, IL-6, etc. that are endogenous factors as well as LPS (lipopolysaccharide) that is derived from outside of the body.
Recently, numerous studies about LPC (lysophosphatidylcholine) and SPC (sphingosylphosphorylcholine) having LPA (lysophosphatidyl acid) or S1P (sphingosine 1-phosphate), which have been known as lipid transmitter, and a choline bound thereto, are being under progress. LPC and SPC have been known to have an important role in functioning not only as intermediates in biosynthesis of cellular membranes, together with LPA and SIP, but also as signaling molecules (Fukushima, N. et al., Annu. Rev. Pharmacol. Toxicol., 41: 507-534, 2001). They are bound to their receptors and induce various cell reactions such as cell proliferation, differentiation, movement, cell death, etc. through several signal transductions (Lynch, K. R. et al., Trends Pharmacol. Sci., 20(12): 473-475, 1999). The receptors to which they are bound are a kind of receptors that are classified as G protein-coupled receptors. Since OGR-1 (orphan G-protein-coupled receptor 1) was for the first time found as a receptor of SPC (Xu, Y. et al., Nat. Cell. Biol., 2(5):264-267, 2000), studies about identifying ligands for GPR4- and G2A receptors having a structure similar to OGR-1 have been conducted. As a result, it was identified that GPR4 recognized SPC and LPC as its ligand and GPR4 promoted cell proliferation by SPC and LPC whereas OGR-1 suppressed cell proliferation by SPC (Zhu, K. et al., J. Biol. Chem., 276(44): 41325-41335, 2001). Moreover, it was reported that G2A had a high affinity to LPC, however, it had a low affinity to SPC (Kabarowski, J. H. et al., Science, 293(5530): 702-705, 2001). G2A is mostly found in lymphocytes and the expression thereof is upregulated by stress and prolonged mitogenic signals. It was reported that in knockout mice that did not have G2A receptors, autoimmune diseases were caused (Le, L. Q. et al., Immunity, 14(5): 561-571, 2001).
Hence, in the course of conducting continuous studies to find out new therapeutic agents for treating inflammatory diseases, the present inventors identified that agonist ligands specific to G2A receptor that exists in neutrophils block suppression of neutrophil apoptosis by inflammation mediators and release of IL-8 (interleukin-8) in neutrophils and monocytes, and exhibit excellent therapeutic effect on an inflammatory disease, especially inflammatory diseases associated with hyperactivity of neutrophil and excessive release of IL-8, or a disease associated with microbial infection, and thus they have completed the present invention.